1. Field of the Invention
This invention relates to the treatment of natural or regenerated cellulose textile materials with dimethylolated carbamates to increase the shrink resistance and wrinkle resistance of said materials.
2. Description of the Prior Art
In the manufacture of textile materials comprising natural and regenerated cellulose, it is common to subject such materials to a finishing step utilizing aminoplast substances in order to provide improved wrinkle resistance and shrink resistance to said textile materials. The treatment of said textile materials with aminoplast-substances involves the impregnation with an aqueous solution or dispersion of an aminoplast substance followed by passing the textile material through squeeze rolls and the subsequent drying and curing at elevated temperatures so as to render the treatment wash-fast. At each stage of processing, the presence of free formaldehyde by which is meant formaldehyde which is present but not bound chemically and is therefore free to volatilize from the textile material, has created a serious problem. The presence of free formaldehyde causes discomfort and sometimes an actual health hazard to those who cut, sew, trim, and press the garment made from the aminoplast-treated textile material.
Of the various aminoplast substances utilized to treat textile material comprising natural or regenerated cellulose, the dimethylolated carbamates are particularly objectionable from the standpoint of providing high amounts of free formaldehyde in textile materials treated therewith. This is perhaps because excess formaldehyde must be used in the preparation in order to obtain the dimethylol derivative. For instance, one mole of methylcarbamate is reacted with 2.25 moles of formaldehyde to produce 0.8 mole of the dimethylolmethylcarbamate. It is apparent that an excess of formaldehyde remains in the reaction product.
In the prior art, various means have been proposed for reducing the free formaldehyde content of dimethylolated carbamate finishing agents for textile materials. For instance, the use of lower molar ratios of formaldehyde to carbamate in synthesis has been suggested. This improvement is achieved at the expense of a lower level of chlorine resistance in the finished fabrics. Another approach to decreased free formaldehyde has been the treatment of the solution of the methylolated finishing agent with a reactant that combines with free formaldehyde and thus binds it, preventing its release during fabric processing. Representative examples of such treatments can be found in U.S. Pat. Nos. 3,749,751; 3,590,100; 3,556,713; 3,597,380; and 3,723,058. These various treatments have not been sufficient to reduce the free formaldehyde to sufficiently low levels which is necessary because release of formaldehyde into the environment is objectionable even at low formaldehyde levels.
In U.S. Pat. No. 3,957,431, there is disclosed a method for diminishing the release of free formaldehyde from textile materials treated with aminoplast-forming substances. In the process, a formaldehyde acceptor is applied to the textile material previously impregnated with an aminoplast-forming substance and dried. Typical formaldehyde acceptors are disclosed as urea, ethylene urea, and propylene urea. A review of this reference indicates that the lowest level of free formaldehyde obtained was 77 parts per million as determined by the AATCC method. It is therefore seen that an improved process for eliminating free formaldehyde in textile materials treated with aminoplast-forming substances is necessary.